Long-Term Surgical Outcomes of Bilateral Symmetrical Superior Oblique Nasal Tenotomy in Patients of Large A-Pattern Exotropia

Abstract

Purpose: To report the long-term outcomes of bilateral symmetrical superior oblique (SO) nasal tenotomy in patients with large A-pattern exotropia (≥25 prism diopter [PD]). Methods: This retrospective study was conducted on 15 patients (aged: 4–28 years) of large A-pattern exotropia. An A-pattern was defined as >10 PD difference between up and down gaze at 6 m by use of the alternate prism cover test. Objective ocular torsion was assessed by fundus photography and subjective torsion by double Maddox rod test. All patients underwent horizontal muscle surgery according to the primary position horizontal deviation and bilateral symmetrical SO nasal tenotomy for A-pattern. Surgical success was defined as postoperative A-pattern of ≤10 PD, the absence of vertical and torsional diplopia, and the absence of V-pattern. The minimum follow-up period was 24 months. Results: A total of 15 patients of large A-pattern exotropia (7 males and 8 females) with a mean age of 17.09 ± 7.9 years were included in the study. All patients had bilateral SO overaction of grade +3 or +4 with a mean preoperative A-pattern of 30.3 ± 3.9 PD. At 24 months of follow-up, esotropia in down gaze (V-pattern) was present in four patients with a mean of 11.25 ± 2.5 PD, (range, 10–15 PD). The rest of the 11 patients maintained successful alignment with a mean A-pattern of 3.18 ± 1.17 PD, (range, 2–5 PD). There was significant A-pattern collapse with a mean of 31 ± 9.1 PD after 2 years of follow-up, which was significantly associated with preoperative A-pattern (Pearson correlation, r = 0.7; t[15] = 4.0; P = 0.002). The mean of pre- and postoperative objective ocular torsion was found to be −0.5 ± 4° and −4.8 ± 3.8° with a mean extorsion effect of 4.67 ± 3.85°. There was a statistically significant difference between pre- and postoperative ocular torsion (°) (t [30] = 5.42; P < 0.001), the change in ocular torsion was significantly associated with preoperative torsion (Pearson correlation, r = 0.5; t [30] = 7.2; P < 0.001). None of the patients had subjective torsion on the double Maddox rod test pre- and postoperatively. Conclusions: Bilateral symmetrical SO nasal tenotomy is effective in cases with large A-pattern (>25 PD). The reduction of A-pattern and postoperative change in fundus torsion have a positive correlation with preoperative A-pattern and preoperative torsion, respectively.